Subvocalization, also known as (implicit speech, inner vocalization, or subvocal articulation), is an inner speech characterized by minute movements in the larynx and other muscles involved in the articulation of speech. Subvocalization plays a definitive role in the encoding and processing of verbal and acoustic information into memory storage. It is one of the components of Baddeley and Hitch's phonological loop proposal which accounts for the storage of these types of information into short-term memory.[1].

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It occurs during silent reading.[2]Neuropsychologia, 33(11), 1433-1454.</ref> where it is is defined as the internal speech made when reading a word, thus allowing the reader to imagine the sound of the word as it is read.[3] This is a natural process when reading and helps to reduce cognitive load, and it helps the mind to access meanings to enable it to comprehend and remember what is read.[4] Although some people associate subvocalization with moving one's lips, the actual term refers primarily to the movement of muscles associated with speaking, not the literal moving of lips. Most subvocalization is undetectable (without the aid of machines) even by the person doing the subvocalizing.[4]

Advocates of speed reading generally claim that subvocalization places extra burden on the cognitive resources, thus, slowing the reading down.[5] Speedreading courses often prescribe lengthy practices to eliminate subvocalizing when reading. Normal reading instructors often simply apply remedial teaching to a reader who subvocalizes to the degree that they make visible movements on the lips, jaw, or throat.[6]

No evidence exists that normal non-observable subvocalizing will negatively affect any reading process [3] At the more powerful rates (memorizing, learning, and reading for comprehension), subvocalizing is very detectable by the reader. At the less powerful, faster rates of reading, (skimming, and scanning) subvocalization is less detectable. For competent readers, subvocalizing to some extent even at scanning rates is normal.[6]

It may be impossible to totally and permanently eliminate subvocalization because people learn to read by associating the sight of words with their spoken sounds. Sound associations for words are indelibly imprinted on the nervous system—even of deaf people, since they will have associated the word with the mechanism for causing the sound or a sign in a particular sign language.[citation needed] Subvocalizing is an inherent part of reading and understanding a word, and micro-muscle tests suggest that subvocalizing is impossible to permanently eliminate. Attempting to stop subvocalizing is potentially harmful to comprehension, learning, and memory [citation needed]. At the more powerful reading rates (100-300 words per minute), subvocalizing can be used to improve comprehension.[4]

Subvocalizing or actual vocalizing can indeed be of great help when one wants to learn a passage verbatim. This is because the person is repeating the information in an auditory way, as well as visually seeing the piece on the paper.

Subvocalization has been considered as far back as 1868.[2] Only in 1899 did an experiment take place to record movement of the larynx through silent reading by a researcher named Curtis, who concluded that silent reading was the only mental activity that created considerable movement of the larynx.[2]

In 1950 Edfelt reached a breakthrough when he created an electrically powered instrument that can record movement. He concluded that newer techniques are needed to accurately record information and that efforts should be made to understand this phenomenon instead of eliminating it.[2] After failed attempts trying to reduce silent speech in study participants, in 1952, it came to the conclusion that silent speech is a developmental activity which reinforces learning and should not be disrupted during development, in 1960 Edeflt seconded this opinion.[2]

EMG can be used to show the degree to which one is subvocalizing[7] or to train subvocalization suppression.[11] EMG is used to record the electrical activity produced by the articulatory muscles involved in subvocalization. Greater electrical activity suggests a stronger use of subvocalization.[7][11] In the case of suppression training, the trainee is shown their own EMG recordings while attempting to decrease the movement of the articulatory muscles.[11] The EMG recordings allows one to monitor and ideally reduce subvocalization.[11]

In concurrent speaking tasks, participants of a study are asked to complete an activity specific to the experiment while simultaneously repeating an irrelevant word.[8] For example, one may be asked to read a paragraph while reciting the word "cola" over and over again.[10] Speaking the repeated irrelevant word is thought to preoccupy the articulators used in subvocalization.[8] Subvocalization, therefore, cannot be used in the mental processing of the activity being studied. Participants who had undergone the concurrent speaking task are often compared to other participants of the study who had completed the same activity without subvocalization interference. If performance on the activity is significantly less for those in the concurrent speaking task group than for those in the non-interference group, subvocalization is believed to play a role in the mental processing of that activity.[8][9][10][11] The participants in the non-interference comparison group usually also complete a different, yet equally distracting task that does not involve the articulator muscles [9][11](i.e. tapping). This ensures that the difference in performance between the two groups is in fact due to subvocalization disturbances and not due to things such as task difficulty or a divide in attention.[9][11]

Shadowing is conceptually similar to concurrent speaking tasks. Instead of repeating an irrelevant word, shadowing requires participants to listen to a list of words and to repeat those words as fast as possible while completing a separate task being studied by experimenters.[8]

Techniques for subvocalization interference other may also include counting,[9][10] chewing [12] or locking one's jaw while placing the tongue on the roof of one's mouth.[12]

The exploration into the evolutionary background of subvocalization is currently very limited. There is however hope for exciting new discoveries in the near future. The little known is predominantely about language acquisition and memory. Evolutionary psychologists suggest that the development of subvocalization is related to modular aspects of the brain.[13] There has been a great amount of exploration on the evolutionary basis of universal grammar.[13] The idea is that although the specific language one initially learns is dependent on one's culture, all languages are learned through the activation of universal ‘language modules’ that are present in each of us.[13] This concept of a modular mind is a prevalent idea that will help explore memory and its relation to language more clearly, and possibly illuminate the evolutionary basis of subvocalization. The most lucrative evidence for the mind having modules for superior function is the example that hours may be spent toiling over a car engine in an attempt to flexibly formulate a solution, but, in contrast, extremely long and complex sentences can be comprehended, understood, related and responded to in seconds.[13] The specific inquiry into subvocalization may be minimal right now but there is a lot to investigate in regards to the modular mind.

Subvocalization is a topic that has much to be discovered and when inquiring as to what structures mediate this process alone, it is safe to say that it is not just one part of the brain, and that no one test will uncover this completely. Studies often use event-related potentials; brief changes in an EEG (electroencephalography) to show brain activation, or fMRIs.

Subvocalization is related to inner speech; when we use inner speech there is bilateral activation in predominantly the left frontal lobe.[14] This activation could suggest that the frontal lobes may be involved in motor planning for speech output.[14]

Subvocal rehearsal is controlled by top down processing;[14] conceptually driven, it relies on information already in memory.[15] There is evidence for significant left hemisphere activation in the inferior and middle frontal gyri and inferior parietal gyrus during subvocal rehearsal.[16]Broca’s area has also been found to have activation in other studies exploring subvocal rehearsal.[17]

Silent speech-reading and silent counting are also examined when experimenters look at subvocalization. These tasks show activation in the frontal cortices, hippocampus and the thalamus for silent counting.[14] Silent-reading activates similar areas of the auditory cortex that are involved in listening.[14]

Finally, the phonological loop; proposed by Baddeley and Hitch as “being responsible for temporary storage of speech-like information”[18] is an active subvocal rehearsal mechanism, activation originating mostly in the left hemispheric speech areas: Broca’s, lateral and medial premotor cortices and the cerebellum.[19]